Polymers with higher melt indexes typically have lower viscosities and therefore do not have appropriate melt strengths suitable for profile extrusions. Such polymers pour out of the profile extrusion mold and do not hold shapes well. The polymers used for injection molding usually have melt indexes between 4 and 30 as compared to between 0.1 and 2 for profile extruding. Many polymers used in injection molding or other molding processes may be desirable for use in profile extrusion due to characteristics such as biodegradability, compatibility with additional components, “green” designation, etc., but are not able to be profile extruded due to their inherently high melt indexes. Many biopolymers, such as polyhydroxyalkanoate (PHA) and polylactic acid (PLA), have poor extensional viscosity which is important for profile extrusion. In profile extrusion, the polymers used must maintain a relatively high degree of melt strength and resist being “pulled or drawn” so as to retain shape.
Plasticizers are sometimes used to lower the melting point of a polymer and allow for lower processing temperatures. By using a plasticizer, the inherent mechanical properties of the polymer is changed, such as making it more flexible. The use of a plasticizer allows for lower processing temperatures, but also interferes with the polymer's viscosity, thus inhibiting the extrusion.
Polyvinyl chloride (PVC) is often used as the material of choice for architectural, fenestration and furniture components. Unfortunately, PVC has more recently been labeled as a harmful or poisonous plastic. Its manufacturing process produces harmful chemicals and expends high levels of energy. For recycling purposes, PVC may release harmful gases when burned and is not a substance that will readily compost.